customize-mark-to-save

customize-mark-to-save is a compiled Lisp function in `custom.el'.
(customize-mark-to-save SYMBOL)
Mark SYMBOL for later saving.
If the default value of SYMBOL is different from the standard value,
set the `saved-value' property to a list whose car evaluates to the
default value. Otherwise, set it to nil.
To actually save the value, call `custom-save-all'.
Return non-nil if the `saved-value' property actually changed.